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SubjectRe: [mm PATCH 2/6] RCU: softirq for RCU


Finally, RCU gets its own softirq. With it being used extensively,
the per-cpu tasklet used earlier was just a softirq with overheads.
This makes things more efficient.

Signed-off-by: Dipankar Sarma <dipankar@in.ibm.com>
---


diff -puN include/linux/interrupt.h~rcu-softirq include/linux/interrupt.h
--- linux-2.6.20-rc3-mm1-rcu/include/linux/interrupt.h~rcu-softirq 2007-01-15 15:36:43.000000000 +0530
+++ linux-2.6.20-rc3-mm1-rcu-dipankar/include/linux/interrupt.h 2007-01-15 15:36:43.000000000 +0530
@@ -236,6 +236,7 @@ enum
#ifdef CONFIG_HIGH_RES_TIMERS
HRTIMER_SOFTIRQ,
#endif
+ RCU_SOFTIRQ /* Preferable RCU should always be the last softirq */
};

/* softirq mask and active fields moved to irq_cpustat_t in
diff -puN kernel/rcuclassic.c~rcu-softirq kernel/rcuclassic.c
--- linux-2.6.20-rc3-mm1-rcu/kernel/rcuclassic.c~rcu-softirq 2007-01-15 15:36:43.000000000 +0530
+++ linux-2.6.20-rc3-mm1-rcu-dipankar/kernel/rcuclassic.c 2007-01-15 15:36:43.000000000 +0530
@@ -69,7 +69,6 @@ DEFINE_PER_CPU(struct rcu_data, rcu_data
DEFINE_PER_CPU(struct rcu_data, rcu_bh_data) = { 0L };

/* Fake initialization required by compiler */
-static DEFINE_PER_CPU(struct tasklet_struct, rcu_tasklet) = {NULL};
static int blimit = 10;
static int qhimark = 10000;
static int qlowmark = 100;
@@ -215,7 +214,7 @@ static void rcu_do_batch(struct rcu_data
if (!rdp->donelist)
rdp->donetail = &rdp->donelist;
else
- tasklet_schedule(&per_cpu(rcu_tasklet, rdp->cpu));
+ raise_softirq(RCU_SOFTIRQ);
}

/*
@@ -367,7 +366,6 @@ static void rcu_offline_cpu(int cpu)
&per_cpu(rcu_bh_data, cpu));
put_cpu_var(rcu_data);
put_cpu_var(rcu_bh_data);
- tasklet_kill_immediate(&per_cpu(rcu_tasklet, cpu), cpu);
}

#else
@@ -379,7 +377,7 @@ static void rcu_offline_cpu(int cpu)
#endif

/*
- * This does the RCU processing work from tasklet context.
+ * This does the RCU processing work from softirq context.
*/
static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
struct rcu_data *rdp)
@@ -424,7 +422,7 @@ static void __rcu_process_callbacks(stru
rcu_do_batch(rdp);
}

-static void rcu_process_callbacks(unsigned long unused)
+static void rcu_process_callbacks(struct softirq_action *unused)
{
__rcu_process_callbacks(&rcu_ctrlblk, &__get_cpu_var(rcu_data));
__rcu_process_callbacks(&rcu_bh_ctrlblk, &__get_cpu_var(rcu_bh_data));
@@ -488,7 +486,7 @@ void rcu_check_callbacks(int cpu, int us
rcu_bh_qsctr_inc(cpu);
} else if (!in_softirq())
rcu_bh_qsctr_inc(cpu);
- tasklet_schedule(&per_cpu(rcu_tasklet, cpu));
+ raise_softirq(RCU_SOFTIRQ);
}

static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp,
@@ -511,7 +509,7 @@ static void __devinit rcu_online_cpu(int

rcu_init_percpu_data(cpu, &rcu_ctrlblk, rdp);
rcu_init_percpu_data(cpu, &rcu_bh_ctrlblk, bh_rdp);
- tasklet_init(&per_cpu(rcu_tasklet, cpu), rcu_process_callbacks, 0UL);
+ open_softirq(RCU_SOFTIRQ, rcu_process_callbacks, NULL);
}

static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
_
-
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